Various influences of ultraviolet rays to skin, such as rapid aging of the skin, are recently well known. The ultraviolet rays included in sunlight are classified into a long wavelength ultraviolet ray having a wavelength from 400 nm to 320 nm as UV-A, a medium wavelength ultraviolet ray having a wavelength from 320 nm to 290 nm as UV-B, and a short wavelength ultraviolet ray having a wavelength of not more than 290 nm as UV-C in a field of skin science.
Since most of the ultraviolet rays usually irradiated human body originate in sunlight, the UV-C are absorbed by the ozonosphere and the body is mainly influenced by the UV-A and UV-B.
Among these, the UV-B forms erythema or blister and causes aggravation of melanin formation and chromatosis when the skin is irradiated with the UV-B over a certain level.
In order to prevent aging of human skin and generation or increase of blots and flecks thereon, it is very important to protect human skin from the UV-B, and various types of UV-B absorbent have been developed.
The prior UV-B absorbents used for practical application include a PABA derivative, a cinnamic acid derivative, a salicylic acid derivative, a benzophenone derivative, an urocanine derivative, a camphor derivative, and a heterocyclic derivatives.
These types of UV-B absorbents are generally mixed in external preparations for skin such as cosmetics or quasi drugs.
The prior types of UV-B absorbents, however, are oil soluble in most cases and their solubility in water is very low, so their applications have been limited to a narrow area. As a water soluble UV-B absorbent, only 2-hydroxy-4-methoxy-5-sulfoxonium benzophenone sodium salt has been known, however this had not enough ultraviolet ray absorptivity.